Understanding Rust Error E0077

Overview of Rust Error E0077

Rust Error E0077 occurs when a tuple struct's element is not a machine type while using the #[simd] attribute. This is because the elements inside the tuple struct need to be machine types to perform SIMD (Single Instruction, Multiple Data) operations on them.

Erroneous Code

#![allow(unused)]
#![feature(repr_simd)]

fn main() {
    #[repr(simd)]
    struct Bad(String); // error!
}

In the code above, the tuple struct 'Bad' has a String element. Since String is not a machine type, the compiler throws Error E0077.

Fixing the Error

To fix this error, you need to use machine types for elements in the tuple struct when using the #[simd] attribute. Machine types include integer and floating-point types like u32, i32, f32, and f64, which can be used with SIMD operations.

Fixed Code

#![allow(unused)]
#![feature(repr_simd)]

fn main() {
    #[repr(simd)]
    struct Good(u32, u32, u32, u32); // ok!
}

In the fixed code, the error is resolved by modifying the tuple struct 'Good' to contain four elements of type u32.

Conclusion

This article explained Rust error E0077 in detail, discussing the common mistake of using non-machine types with the #[simd] attribute in tuple structs and how to fix it. Ensure that all elements in a tuple struct are machine types when using #[simd] for correct SIMD operation usage.